1. Field of the Invention
This invention relates generally to the field of refrigeration systems, and more particularly to an electronically-controlled process fluid chilling system including a chiller and a dry cooler providing a heat exchange between an exchange medium and the process fluid flowing through the dry cooler. And even more particularly, embodiments of the present invention also relate to a microprocessor-based controller for implementing the system.
2. Description of Related Art
Conventional refrigeration systems utilize a refrigerant that removes heat from a fluid used for cooling applications and ejects the removed heat to a heat sink in an ambient environment of the refrigeration system. The heat sink can be ambient air or a fluid such as water from a cooling tower in thermal communication with the refrigeration system. An example of such a refrigeration system is a water chiller that transfers thermal energy from water to the refrigerant during a chilling cycle to chill the water. The chilled water is then transported through a piping system to remove thermal energy from a warm environment or a piece of processing equipment as desired.
In operation, these conventional refrigeration systems take advantage of state changes experienced by the refrigerant to remove the thermal energy from a process fluid and subsequently release that removed thermal energy to ambient air, water from a cooling tower or other suitable ambient environment of the refrigeration system. But regardless of the heat sink to which thermal energy is removed from the refrigerant, a compressor for elevating the pressure of the refrigerant must be operational to chill the process fluid.
Continuing with the example of a water chiller, a compression type water chiller draws low-pressure refrigerant gas into a compressor, where it is compressed and discharged as a high-pressure refrigerant gas. Due to the relationship between the pressure and temperature of the refrigerant, the temperature of the refrigerant gas is also raised to an elevated temperature above the temperature of the low-pressure refrigerant gas when it is introduced to the compressor. This hot refrigerant gas flows through a conduit to be introduced to a condenser. The hot refrigerant gas condenses as it travels through the conduit and in the condenser before entering an evaporator to which the water is also introduced during the chilling cycle. As the liquid refrigerant and water to be chilled travel through the evaporator, the liquid refrigerant rapidly expands and evaporates into a gas. The required thermal energy, commonly referred to as the latent heat of vaporization, to accomplish this state change of the refrigerant from liquid to gas is drawn from the water being chilled, thereby chilling the water.
Large refrigeration systems often demand significant chilling capacity to provide a sufficient amount of chilled fluid to adequately cool large processes and process equipment operating at very high temperatures. To meet such demands the refrigeration system discussed above requires large compressors which tend to be inefficient and costly. Further, these compressors must be continuously operated to satisfy chilling demands, leading to large operational costs.
To minimize the costs associated with large refrigeration systems in chilling water, cooling towers have been employed to directly chill water used in industrial cooling applications. Cooling towers direct air through a stream of water in a direction that is perpendicular to the flow direction of the water. The airflow causes at least some of the water to evaporate, thereby chilling the water as it flows through the cooling tower. However, cooling towers are limited in their ability to adequately chill water based on the temperature and relative humidity in their ambient environment. This prohibits the use of cooling towers as options for chilling water or other process fluids in many geographic regions. Further, processes that utilize water directly from a cooling tower to cool process equipment typically require the water to be conditioned to remove foreign matter collected from the water while it was exposed to the ambient environment during cooling before being transported to the equipment to be cooled.
Accordingly, there is a need in the art for a process fluid chiller for cooling a process fluid. The chiller can optimize efficiency by utilizing a secondary fluid in a closed-loop secondary cooler, and can optionally be responsive to one or more sensed environmental conditions to adjust operation of the refrigeration system. Further, the chiller can optionally include a microprocessor-based control unit for governing operation of the chiller according to application specific computer-executable instructions.